President Obama spoke to the families of the victims of the Navy Yard shooting Sunday, once again taking on the role of "comforter-in-chief" in another mass killing.

The president appeared stern as he spoke at a memorial service for the victims, where he called for "basic common sense action" to reduce gun violence and said Americans should not become "resigned" to periodic mass shootings.

Obama did not, however, mention any proposed legislative changes and instead said the American people must demand change.

The killing of 12 people at the Washington Navy Yard last week was the sixth mass shooting since the president took office.

"No other advanced nation endures this kind of violence, none," Obama said. "Murder rate with guns is 10 times what it is in developed nations. ... It comes about because of decisions we make or fail to make. It falls upon us to make it different."

There have been five prior mass shootings since the president assumed office: Binghampton, N.Y., (2009); Fort Hood, Texas, (2009); Tucson, Ariz., (2011); Aurora, Colo., (2012); and most recently the killing of 20 children and six adults in an elementary school in Newtown, Conn., last December.

"It ought to be a shock to all of us," said Obama of Monday's shooting at the Washington Navy Yard. "It ought to obsess us. It ought to lead to some sort of transformation."

Obama cited the United Kingdom and Australia as examples of countries that successfully enforced strict gun laws after mass shootings that have resulted in virtually no subsequent mass shootings.

Obama also took time to mention each victim by name and talk a bit about their lives, including Richard Michael Ridgell, who coached his daughter's softball team, and Frank Kohler, who gave a dictionary to every third-grader in his county.

At one point the president appeared to pause for a moment, overcome with emotion, when he mentioned Arthur and Priscilla Daniels.

Arthur Daniels, 51, was killed in the Navy Yard shooting. Four years earlier Daniels' 14-year-old son was killed in a shooting in Washington D.C.

"I can't believe this is happening again," said Obama, quoting Priscilla Daniels. The couple had been married for 30 years.

Obama acknowledged that the "politics" of gun control was difficult but implored Americans not to accept that political gridlock would prevent change.

"I do not accept that we cannot find a common-sense way to preserve our traditions, including our basic Second Amendment freedoms and the rights of law-abiding gun owners, while at the same time reducing the gun violence that unleashes so much mayhem on a regular basis," said Obama.

Before Obama spoke Washington D.C. Mayor Vincent Gray said gun violence had become an "everyday fact of life" in Washington, D.C., and that easy access to guns had to stop.

"Our country is drowning in a sea of guns," Gray said. "It's a fact of life which we must stop accepting."

Speaking before Gray, Vice Admiral William Hilarides, the commander of the Naval Sea Systems Command, took issue with the 12 victims being classified as civilians and contractors. Citing their contributions to the Navy, Hilarides called them "service members" who served with honor and were "just as committed as anyone in uniform."

The Naval Sea Systems Command is headquartered in building 197 where Aaron Alexis carried out the shooting rampage on Monday.

According to The Associated Press, the Navy expected roughly 4,000 people for the memorial service, which was closed to the public. Families of the victims sat in the front row and both families and naval officers were seen breaking down during the service.

One young woman with red hair sitting beside the first lady appeared to sob through nearly all of the memorial service. After the service the president and first lady hugged families of the victims.

For the president, such somber occasions have become all too familiar.

Obama has spoken at the memorials for four of the past five mass shootings. And although he did not attend the formal program in Aurora, he met personally with the families of the dozen killed and 58 wounded on the day of that service.

On the day of the Navy Yard shooting the president expressed his frustration with the high frequency of such tragedies when he called it, "yet another mass shooting," and again hinted at the limits of his power in a televised interview the following day.

Speaking with Spanish-language network Telemundo he suggested that stronger background checks on gun purchases might have prevented this latest attack.

"Initial reports indicate that this is an individual who may have had some mental health problems," he said. "The fact that we do not have a firm enough background-check system is something that makes us more vulnerable to these kinds of mass shootings."

A May ABC News/Washington Post poll found 83 percent of Americans support expanded and strengthened checks for all sales, but movement on heightened gun control remains stalled in Congress.